GRIFFIN, W. TIMOTHY, Golder Associates Inc., Richland, WA; T. J. PHELPS, Oak Ridge National Laboratory, Oak Ridge, TN; F. S. COLWELL, Idaho National Engineering Laboratory, Idaho Falls, ID; R. M. LEHMAN, Idaho National Engineering Laboratory, Idaho Falls, ID; B. F. RUSSELL, Golder Associates Inc., Los Alamos, NM; J. P. McKINLEY, Battelle Pacific Northwest Laboratory, Richland, WA; and T. O. STEVENS, Battelle Pacific Northwest Laboratory, Richland, WA

ABSTRACT: Subsurface Microbial Ecology of the Taylorsville Triassic Basin, King George County, Virginia

University and national laboratory researchers from the U.S. Department of Energy's Subsurface Science Program recently teamed with Texaco's Frontier Exploration Department, to collect sidewall cores for microbiological analyses from Texaco's Thorn Hill #1 exploration well in King George Co., Virginia. Upper Triassic fluvial and lacustrine sands, silts, and clays were targeted for the same reasons that make them attractive exploration targets, including 1) potential for high organic carbon, 2) potential for permeable host rock, and 3) structural and stratigraphic seals that isolate indigenous communities from younger formation waters. Rigorous quality control procedures were implemented to ensure sample integrity, including 1) monitoring microbiological characteristics of drilling flu ds at regular intervals, 2) introduction of perfluorocarbon tracers, 3) processing field samples in an anaerobic glove-bag, and 4) initiation of laboratory analyses within 48 hours. Analytical results indicated little or no contamination of the samples, and that changes in the subsurface microbial community occurred with depth. Mesophilic aerobes, typical of shallow subsurface sediments, were replaced by obligately anaerobic thermophilic microorganisms with depth. Samples obtained below

8,000 feet total depth exhibited sulfate-, iron-, and manganese-reducing, fermentative, and methanogenic anaerobes capable of growth at in situ temperatures (>50 degrees C) and in brackish conditions. This research may provide insights into chemical and fuel production and modification, as well as development of microbially enhanced oil recovery and bioremediation technologies.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.